During the wet season, Holsworth’s Grunter is dark bluish-brown, becoming greyish to silver during the dry season. The species is darker above, becoming paler below.Juveniles are white below, with a bluish-silvery stripe below the eye to the snout, a dark blotch on the gill cover, a dark margin on the scale margins, and dark fins occasionally with a purple tinge. No stripes were observed on the sides of juveniles or adults.

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Distribution

Occurs throughout the Ord, Penticost, and Durack rivers in the eastern Kimberley region, Western Australia, and the Victoria River, Northern Territory.Adults prefer deeper, slow flowing sections of creeks and rivers, along with still waters and billabongs. Juveniles inhabit shallow, still waters or occasionally riffle habitats. The species has been found in clear and turbid waters, over rocky and muddy substrates, often where algae is abundant. Recorded in water temperatures up to 36°C. Individuals have been seen shoaling in the middle of the water column around snags, sometimes with the Lake Bonaparte Grunter, Syncomistes bonapartensis.

Colour

Body dark bluish-brown overall during wet season, greyish to silver overall during dry season. Darker dorsally, becoming lighter along the ventral surface. Juveniles white on ventral surface. A blueishsilvery stripe running below eye to snout. Opercle and subopercle with a dark blotch extending ventrally from opercular spine. Posterior scale margins have a dark band. All fins dark, occasionally with a purple tinge. No stripes were observed on the sides of juveniles or adults.

Feeding

Feeds mostly on filamentous algae that is scraped off rocks with specially modified teeth.

Biology

Individuals are sexually mature at 90–100 mm and spawning occurs during the wet season, following a major flood. The eggs are large (~3 mm) and non-adhesive.

Etymology

The specific name holsworthi honours Bill Holsworth whose foundation financed the expedition on which this species was found, as well as providing ongoing support for doctoral research into the ecology, management and natural history of Australian wildlife.